Various attempts have been made to provide tables and other work surfaces having mechanisms for varying the height of the work surface relative to the floor and to the user.
The majority of conventional adjustable height tables are either simple in construction yet require lots of manual labor to change the heights thereof or are extremely complex electrical and electromechanical devices that are prohibitively expensive for most applications.
U.S. Pat. No. 5,107,775 to Langlais et al. discloses a school desk having hollow, tubular legs with a variety of vertically spaced holes drilled therethrough. Mating outer sleeves are provided having similar holes through which screws are inserted and secured by nuts. To adjust the height of the work surface of the desk, each sleeve must be released, changed in height, and reattached to its associated tubular leg.
German Patent No. 904,938 to Gortz et al., discloses an adjustable height table leg including an inner support foot which can be variably fixedly retained relative to the tubular leg by use of a number of spring-loaded pins which engage with appropriate holes in an outer hollow leg. Although this device may be more easily manually adjusted than the Langlais et al. device, described immediately above, it is still labor-intensive and unsuitable for applications where frequent height adjustment of a work surface is required.
U.S. Pat. No. 2,792,944 to Drommer discloses a bookkeeping stand having pins mounted on a spring-loaded member for being normally biased into engagement with a plurality of vertically spaced holes extending along the length of the Drommer corner posts (legs). The Drommer device is simple and efficient, yet likely inappropriate for carrying heavy loads on its work surface.
A U-shaped adaptive work station is disclosed in U.S. Pat. No. 4,894,600 to Kearney. The Kearney work tabletop is height adjustable, yet its movement is dependent on an outside source of electrical power. A suggestion is made in the Kearney patent that a safety mechanism which stops downward travel to prevent injuries to a user's legs when seated with his or her legs underneath the work station be provided. No disclosure is made in Kearney as to how one might make a substantially purely mechanical height adjustable work station.
Accordingly, there is a need for a height adjustable work surface or table which is easily used, carries heavy loads, is reliable, and overcomes the drawbacks of the prior art devices.
The use of the term "table" is for convenience only, as all movable work surfaces and table-like devices are intended to be within the scope of the invention. Likewise, the use of the terms "ground", "floor", and "support", for example, are intended to encompass all supporting surfaces and other objects which support the invention and relative to which the working surface or tabletop according to the invention will move.